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cgroups: add cpu_relax() calls in css_tryget() and cgroup_clear_css_refs() 

css_tryget() and cgroup_clear_css_refs() contain polling loops; these
loops should have cpu_relax calls in them to reduce cross-cache traffic.

Signed-off-by: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Paul Menage 2009-01-29 14:25:21 -08:00 committed by Linus Torvalds
parent 1404f06565
commit 804b3c28a4
2 changed files with 6 additions and 2 deletions
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1
include/linux/cgroup.h
View File

@ -99,6 +99,7 @@ static inline bool css_tryget(struct cgroup_subsys_state *css)
while (!atomic_inc_not_zero(&css->refcnt)) { while (!atomic_inc_not_zero(&css->refcnt)) {
if (test_bit(CSS_REMOVED, &css->flags)) if (test_bit(CSS_REMOVED, &css->flags))
return false; return false;
cpu_relax();
} }
return true; return true;
} }

7
kernel/cgroup.c
View File

@ -2509,7 +2509,7 @@ static int cgroup_clear_css_refs(struct cgroup *cgrp)
for_each_subsys(cgrp->root, ss) { for_each_subsys(cgrp->root, ss) {
struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id]; struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
int refcnt; int refcnt;
do { while (1) {
/* We can only remove a CSS with a refcnt==1 */ /* We can only remove a CSS with a refcnt==1 */
refcnt = atomic_read(&css->refcnt); refcnt = atomic_read(&css->refcnt);
if (refcnt > 1) { if (refcnt > 1) {
@ -2523,7 +2523,10 @@ static int cgroup_clear_css_refs(struct cgroup *cgrp)
* css_tryget() to spin until we set the * css_tryget() to spin until we set the
* CSS_REMOVED bits or abort * CSS_REMOVED bits or abort
*/ */
} while (atomic_cmpxchg(&css->refcnt, refcnt, 0) != refcnt); if (atomic_cmpxchg(&css->refcnt, refcnt, 0) == refcnt)
break;
cpu_relax();
}
} }
done: done:
for_each_subsys(cgrp->root, ss) { for_each_subsys(cgrp->root, ss) {